The long-term goal of this project is to understand the structural and functional basis for vascular smooth muscle (VSM) mechanotransduction. The ability of VSM to transduce physical forces such as pressure or stretch into arterial constriction (myogenic behavior) is vital for maintaining peripheral resistance and cerebral blood flow autoregulation. This application has been revised to take a more systematic and focused approach towards understanding myogenic behavior by examining three principal phenomena: the development of myogenic tone, myogenic reactivity and forced dilation. Our central hypothesis is that cerebral artery myogenic tone and reactivity are effected via a series of complementary, pressure-induced changes in membrane function (membrane potential, calcium entry), myofilament regulatory mechanisms (calcium sensitivity) and cytoskeletal structure (actin polymerization). Aim 1 to understand the biophysical and mechanistic determinants of MT development. The discrete and measurable event occurs once a sufficient pressure or stretch has been imposed upon the vessel, and results in the activation of cellular mechanisms, such as membrane depolarization and calcium entry, that produce sustained arterial constriction or tone. We will test the hypothesis that the appearance of myogenic tone can be related to a specific level of vascular wall deformation, and is associated with a threshold membrane potential and/or cytosolic calcium concentration. The role of these factors, and of their modulation by PKC activation/inhibition in determining the extent of tone will also be investigated, as will the hypothesis that development of tone is associated with significant actin polymerization. Aim 2 is to investigate the factors that modulate myogenic reactivity (dphi/dP) by using intact and permeabilized vessels, and to define the autoregulatory efficiency of MR as a function of activation/inhibition of different signal transduction components suspected to play a major role in myogenic reactivity. By using complementary approaches to evaluate functional (reactivity, membrane potential, cytosolic calcium concentration) and structural changes (measuring G actin fluorescence and F actin by using laser confocal microscopy and electron microscopy; manipulating the state of the cytoskeleton by pharmacological polymerizing/depolymerizing agents), we hope to understand the relationship between transmural pressure and arterial constriction (myogenic reactivity). Finally, the sudden and dramatic failure of this adaptive vascular mechanism in response to acute hypertension (forced dilation, a cardinal event in hypertensive encephalopathy- AIM 3) will be investigated to determine the role of ionic (VM, calcium), enzymatic (PKC) and cytoskeletal (actin) factors in its genesis and outcome.